Fix the ground first, a bad ground causes all sorts of problems. Also, you could make your speakers bottom out and also blow even if you are sending less wattage to the speakers. If you are pushing your amp past its limits (gain knob set very high) you will be sending a clipped signal to your speakers which could damage them. After you fix your ground, set your gain properly. The conventional way to set the gain is to turn the knob all the way down initially and turn your stereo up as loud as you would normally listen to it, then turn the gain up to the point right before distortion.